2.2. Casting films and capsule preparation
After degassing, 50 mL of a solution was poured onto a polyethylene
plate (10 cm
×
15 cm), which was kept level to control film
thickness. The cast film was dried overnight at 37 ◦C, similar to capsule
preparation. The dry films were peeled from the plate, placed in
a desiccator containing saturated sodium bromide (NaBr) solution,
and stored at 56% RH and 23 ◦C until required for analysis. Separate
control films of pure gelatin and pure starch were prepared in the
same way. The weight of the dry films was measured daily until no
further measurable weight change was observed, and the thickness
of the films was recorded using a micrometer. All films were about
0.3 mm thick with about 8% SD.
Capsules were prepared by dipping stainless steel mold pins
(cylindrical, 7 mm diameter) into the solutions and then drying at
37 ◦C, as described in detail previously (Jones, 2004a). Drying time
depended on capsule rigidity, and those containing a higher concentration
of starch required a longer drying time, as starch has a
stronger hydroxyl bond with water than gelatin. The drying time
was increased gradually from 30 to 50 min with increasing starch
content from 0 to 50%. Processability was determined by evaluated
the viscosity and gelation temperature of the various blends.
An infra-red heating balance (Model DHS-20) was used to measure
moisture content in samples through heating samples to
110 ◦C for 20 min.